Machine structure

ABSTRACT

A lightweight structure for the base of a co-ordinate measuring machine is formed of a triangulated space frame arrangement using carbon fibre reinforced plastics bars (30) having a near zero coefficient of thermal expansion. The frame arrangement may be covered by a skin extending across one or more faces of the frame members to form a closed structure.

This invention relates to apparatus for measuring the distribution inspace of physical properties of a workpiece using a co-ordinate system(hereinafter referred to as a "measuring apparatus" for ease ofdescription) and is particularly concerned with high accuracy measuringand checking apparatus.

According to the present invention there is provided a measuringapparatus as hereinbefore defined comprising at least in part aplurality of frame components which either have such inherent propertiesor are so interconnected as to define a rigid but relatively lightweightstructure.

Preferably the frame components are interconnected in a triangulatedspace frame arrangement. Preferably also the frame components areconstructed from a carbon fibre composite material.

Cover means may extend across the frame components and be connectedthereto, and may comprise a single skin of material across one face ofthe frame components. A further single skin of material may extendwholly or partly across the opposed face of the frame components. Inanother arrangement, the cover means may be one or more panels, at leastsome of which may have a triangulated configuration and may beinterconnected in a triangulated arrangement.

Further the frame components may comprise a plurality of interconnectedpanels, some of which may have a triangular configuration and beinterconnected in a triangulated arrangement, whereby to define a rigidbut relatively lightweight structure.

Preferably the panels are constructed from a carbon fibre compositematerial.

Preferably also at least some of the panels have an open cellularconstruction with skins extending across respective open faces of thecellular construction. The cellular construction may take the form of ahoneycomb. Alternatively the panels may have an infill, for example of afoam plastic material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of part of a co-ordinatemeasuring apparatus; and

FIG. 2 shows schematically part of one embodiment of a structure for anapparatus according to the invention;

FIG. 3 shows schematically a further embodiment of a structure for anapparatus according to the invention;

FIG. 4 shows schematically another embodiment of a structure for anapparatus according to the invention; and

FIG. 5 is a persepctive view of a panel of a further embodiment of thestructure, with part removed to view internally.

Referring to FIG. 1 of the drawings, a three-axis co-ordinate measuringmachine comprises a base 10, and columns 12 supporting a bridge 14 andarranged for movement along the base 10 by means of guideways 16. Thecolumns 12 have guideways 18 for lateral movement of a carriage 20, thelatter mounting a probe which is vertically movable thereon and isadapted to contact the workpiece. Such a machine is conventional.

The base 10 may be formed as a lightweight structure, for example ofsteel or a granite composite as described in our co-pending U.K.Application No. 8808281 entitled "Support Structures", supported asdescribed in our co-pending U.K. Application No. 8808282 entitled"Support Assemblies" now U.S. Pat. No. 5,063,683, and the linearguideways in the machine may comprise tubular guides as also describedin our co-pending U.K. Application No. 8808279 entitled "Linear GuidingApparatus".

A lightweight structure for the columns 12 and the bridge 14 may beformed by a plurality of frame members connected together in atriangulated space frame arrangement, with a cover or single skinextending across one face of the frame members to form a closedstructure.

In a first embodiment of the lightweight structure, shown in FIG. 2, afully triangulated space frame is formed of bars 30 which may be made,for example, from a carbon fibre reinforced plastic material. In such amaterial the carbon fibres may be uni-directional along the bars 30 ormay contain circumferential or helical fibres. The bars 30 may be solidor hollow, or any cross-sectional, configuration, and may contain a coreof another material. In FIG. 2 the apices of a first triangle in a planenormal to a longitudinal axis 32 of the structure are identified by A,B, C. Other such triangles in parallel planes are identifiedrespectively by D, E, F; G, H, J; K, L, M. Each apex of one suchidentified triangle is joined to the adjacent identified triangle by twofurther bars 30.

The embodiment of FIG. 3 has a plurality of the bars 30 arranged in adifferent triangulated space frame. Again the apices of the triangleslocated in planes normal to the longitudinal axis 32 are identifiedrespectively by A, B, C; D, E, F; and G, H, J. Each apex of such anidentified triangle is joined to the apex of each adjacent identifiedtriangle by a bar 30 parallel to the axis 32. Each face of the prismenclosed by the space frame thereby consists of a series of adjacentrectangles and each rectangle has one diagonal bar 30, provided totriangulate the structure.

A triangulated space frame structure as shown in FIG. 4 has a pluralityof the bars 30, forming linked tetrahedra. Those bars 30 identified asA, B; C, D; E, F; and G, H all lie in planes normal to the longitudinalaxis 32 of the structure although at right angles to one another. Eachend of each of the identified bars is connected to the respective endsof the adjacent identified bar, whereby for example A B C D forms atetrahedron of six bars 30. C D E F forms a second tetrahedron with barC D common to both tetrehedra, while a bar B F stabilises the twotetrahedra by forming a tetrehedron B C D F. The tetrahedron A B C D isrepeated as E F G H with a bar D H stabilising two tetrahedra by forminga tetrahedron D E F H. The structure can continue indefinitely in thismanner.

The triangulated space frame arrangement provides an extremely stiff butlightweight structure and the frame members can be formed from materialhaving a near zero coefficient of thermal expansion, for example thecarbon fibre composite material.

In a modification a single skin may extend across the opposed face ofthe frame members or possibly only the joint areas to increase jointstiffness.

In a further embodiment a lightweight structure for the columns 12 andthe bridge 14 may be formed of a plurality of interconnected panels 22(see FIG. 5), each of which has a cellular construction in the form of ahoneycomb 24 extending between double skins 26 located across therespective open faces of the honeycomb 24. Some of the panels 22 may beformed with a triangular configuration and be connected together in atriangulated arrangement. The panels are preferably connected by anysuitable technique using adhesive, and/or mechanical fasteners, andeffectively form a monocoque shell. Such a shell provides an extremelystiff but lightweight structure which can be formed of a material havinga near zero coefficient of thermal expansion, for example carbon fibre.The use of a honeycomb provides for lack of shear between the two skinsof the panel and the use of a double skinned panel prevents bucklingunder compression.

In the modification the panels 22 may be formed of a foam plasticmaterial between the double skins, or any other lightweight structuralmaterial which will transmit shear forces between the skins.

With either type of panel a carbon fibre composite material may beutilised for construction.

In a third embodiment, a lightweight structure for the columns 12 andthe bridge 14 is formed of a plurality of frame members at least some ofwhich are connected together in a triangulated space frame arrangementas described in relation to any of the embodiments of FIGS. 2 to 4.Panels of the type described with reference to FIG. 5 are then connectedacross the frame members to form a closed structure.

Various modifications may be made without departing from the invention.For example the invention is obviously not restricted to the design ofmeasuring machine described and shown or indeed to use with measuringmachines. Also the cellular structure of the panels may take form ofother than a honeycomb.

I claim:
 1. An improved probe support apparatus for a co-ordinatemeasuring machine having a base, a bridge movably mounted on the baserelative to an object to be measured, and a measuring probe supported onthe bridge for movement relative to the object, said support apparatuscomprising:a lightweight, rigid three-dimensional triangulated spaceframe forming a part of the bridge, said space frame comprising aplurality of rigid bars connected adjacent their ends, each of said barsbeing continuous between its respective pair of opposite endconnections, and each end of each bar connected to the respective end ofadjacent bars in a triangulated arrangement; first guideway means formovably guiding and supporting said space frame on the base; and secondguideway means for guiding and supporting the measuring probe on saidspace frame.
 2. The apparatus of claim 1, further comprising means forcovering an open face of said space frame defined by interconnectedbars, said covering means being securely affixed to a plurality of saidbars.
 3. An apparatus according to claim 2, wherein the covering meanscomprises a single skin of material across one open face of said spaceframe.
 4. An apparatus according to claim 2, wherein the covering meanscomprises one or more panels.
 5. An apparatus according to claim 4,wherein at least some of the panels have an open cellular constructionin the form of a honeycomb, with skins extending across respective openfaces of the cellular construction.
 6. An apparatus according to claim4, wherein said panels comprise a cellular construction having the formof a honeycomb.
 7. An apparatus according to claim 4, wherein at leastsome of said panels comprise an open cellular construction in the formof a honeycomb, with skins extending across respective open faces of thecellular construction.
 8. An apparatus according to claim 4, wherein atleast some of said panels comprise a pair of skins and an infill ofstructural material therebetween to transmit shear forces between saidskins.
 9. An apparatus according to claim 8, wherein the structuralmaterial comprises a foamed plastic.
 10. An apparatus according to claim4, wherein at least some of said panels comprise carbon fibre compositematerial.
 11. The apparatus of claim 1, wherein said bars are made froma reinforced composite material which includes a plastic material havingreinforcing fibers embedded therein.
 12. The apparatus of claim 11,further comprising means for covering an open face of said space frame,said covering means being affixed to a plurality of said bars andcomprising composite material.
 13. In combination, an improved probesupport apparatus for a co-ordinate measuring machine having a base, abridge movably mounted on the base relative to an object to be measured,and a measuring probe supported on the bridge for movement relative tothe object, said support apparatus characterized by comprising:alightweight, rigid three-dimensional triangulated space frame forming apart of the bridge, said space frame comprising a plurality of rigidbars connected adjacent their ends, each of said bars being continuousbetween its respective pair of opposite end connections, and each end ofeach bar connected to the respective end of adjacent bars in atriangulated arrangement; first guideway means for movably guiding andsupporting said space frame on the base; and second guideway means forguiding and supporting the measuring probe on said space frame.